An integrated study of Quaternary sedimentary processes on the eastern slope of the Porcupine Seabight, SW of Ireland

A wide range of geophysical and sedimentological investigations on upper slope sediments of the eastern Porcupine Seabight, SW of Ireland, allowed to evaluate the local importance of bottom currents throughout the Upper Paleogene to recent times, as well as the influence of, and interplay with other deep-water sedimentary processes. The tools available for this study mainly allowed to focus on the nature and characteristics of the Quaternary deposits of seismic unit U1, but also documented buried Middle Eocene to Pliocene sediment drifts and sediment waves. A Late Pliocene erosional event (RD1) created a highly irregular discontinuity, observed from the northern part of the Belgica mound province towards the southern Gollum channel and Goban Spur. During this event, the basis of all major channels was created. They remained to be major current pathways, although their seismic characteristics suggest that the vigour of these currents seems to have decreased. The local Quaternary sedimentary environment has been dominated by a dynamic bottom current environment and by the paleotopography of the underlying unit U2. In the Belgica mound province, this unique geographic and hydrodynamic setting was responsible for the deposition of several sediment and contourite drifts. South of the Belgica mounds, the evolution and construction of the flanks of the broad Kings channels is seen to be influenced by downslope flowing currents. It is thought to be affected by periodic turbidite currents, possibly already weakened by northward flowing bottom currents. The main Gollum channel system shows similarities with a submarine fan channel system. The channel deposits are predominantly turbidites and mass-wasting deposits. This study also strengthens the idea that this system is located directly downstream of a (still undiscovered) feeding glacial fluvial system located on the Irish mainland shelf. A SE to NW transect of five long cores demonstrates the variability and distribution of British-Irish Ice Sheet (BIIS) sourced IRD in the Porcupine Seabight. Two cores located on the eastern slope almost exclusively contain BIIS-sourced material. Six ice-rafting events (IRE) were described and can be compared with the North Atlantic Heinrich Events. These regional events carry a very strong BIIS signature with mainly sands originating from Devonian and Carboniferous sandstones. The abundance of the IRD record shows a millennial-scaled disintegration of the BIIS from 25 ka onwards with distinct ice-rafting pulses about 17.4 and 15 ka BP. Moreover, all cores from the Belgica mound province show that the glacial deposits are muddy contourites in which several peak current episodes could be distinguished. More specifically, a core located on the small mounded contourite drift contains an amplified record of this bottom current variability. The presence of a massive sandy contourite between 1500 and 2625 cm suggests that during interglacial times the bottom current regime is similar as the present day situation. A similar conclusion was drawn from a core within one of the Gollum channel heads. During glacial times (especially during the last glacial maximum), turbidity currents were active due to a lowered sea-level. These fine-grained turbidites were deposited in a hemipelagic background sediment with IRD. During interglacial times, reversing bottom currents were active in this channel, creating muddy-silty contourites or even reworking the glacial turbidite deposits